D.1 Sampling and Data Presentation

Statistics begins with two questions: WHO are you measuring (population vs sample) and WHAT are you measuring (discrete vs continuous data). Five named sampling techniques (simple random, convenience, systematic, stratified, quota) with their bias risks. Frequency tables, histograms (touching bars), cumulative-frequency S-curves, box-and-whisker plots. Quartiles Q1/Q2/Q3 and IQR captured graphically and numerically.